Question: "I am a Mormon. Why should I consider becoming a Christian?"

Answer: If we assume that the Bible is the Word of God (both Joseph Smith and Brigham Young believed this), then an examination of the foundational beliefs of Mormonism and the Latter-day Saints (if those beliefs are reliable) should show them to be consistent with what the Bible teaches. Anyone from any religion—or no religion at all—who asks, “Why should I consider becoming a Christian?" should consider the claims of Christianity. For a Mormon asking this question, considering the difference between the tenets of biblical Christianity and LDS philosophy should be the primary area of inquiry. Therefore, we will look at four areas of discrepancy between them.

1) Mormonism teaches a dependence on extra-biblical sources. The Bible teaches that it is sufficient in instruction for all Christian living (2 Timothy 3:16), and God specifically pronounced a curse on anyone who would claim he had authority to add to that which God had revealed in the Bible. In other words, God pronounced his written revelation complete (Revelation 22:18-19). Therefore, there is no reason for God to write more. A God who writes His Scriptures, says they’re complete, and then later realizes He forgot something either didn't plan for the future or didn't know enough to write everything the first time. Such a god is not the God of the Bible. Yet Mormonism teaches that the Bible is only one of four sources, the other three being the Book of Mormon, Doctrine and Covenants, and The Pearl of Great Price. These three came from a single man who declared them to be God-inspired despite their being contrary to the first and only truly inspired text. God Himself pronounced that His written revelation to mankind was complete when He finished the biblical text. To add additional material to Scripture and call it inspired is to contradict God.Read more: http://www.gotquestions.org/Mormon-Christian.html